Meiotic damage-detection checkpoints monitor meiotic progression and ensure the integrity of the genome of the next generation by sensing DNA damage and halting progression until that damage is repaired. If a chromosome aberration, genetic mutation, or external chemical assault leads to unrepaired damage, the appropriate checkpoint shunts the spermatocyte into an apoptotic pathway and, if a sufficient number of spermatocytes are affected, sterility results. While mitotic checkpoints and their controls are reasonably well characterized, the same can not be said of meiotic checkpoints. This proposal addresses some of the unanswered questions in our knowledge of DNA damage-detection checkpoints in mammalian spermatocytes. These essential questions include: How many meiotic checkpoints are there? Where are they located in meiosis? What events do they monitor and what triggers a checkpoint arrest? What meiotic checkpoint proteins have been "borrowed" from the mitotic cycle and are they being used in the same or different ways in meiosis? What are the regulators of the cascades that constitute the meiotic checkpoint pathways? To address these questions we will use a combination of 1) immunohistochemistry (antibody localization) on microspread spermatocytes, 2) histopathological evaluation of testis sections, 3) evaluation of mice with genetic or extrinsic defects, including various chromosomal aberrations, targeted disruption of genes necessary for progression of meiotic events or chemical disruption of meiosis. Our goal is to identify the meiotic checkpoints and their protein components, to elucidate the pathways in which they function, and to determine the activities they monitor and what triggers a checkpoint arrest. Our results will lead to a better understanding of some of the underlying causes of male sterility and could also lead to new insights into development of a male contraceptive.